Shock sensors have been used in motor vehicles to detect a vehicle collision and to activate an electronic circuit for the actuation of safety devices, such as to tension safety belts, to inflate air bags, to shut off fuel systems, to activate radio signals, or to actuate other desired systems. Such shock sensors typically employ a reed switch having ferromagnetic contacts and operate such that the mass of a magnet or ferromagnetic shunt is accelerated by vehicle impact against a biasing and restoring force such as a wire spring or repelling magnet. See, e.g. U.S. Pat. Nos. 4,484,041 and 4,639,563 issued to Andres et al., and Gunther, respectively. The change in magnet position or the resultant shunting causes a change in the magnetic field relative to reed switch sensitivity. The change in magnetic field therefore acts as a means of operating the reed switch contacts.
The shock sensors that employ a reed switch typically have a carriage that slidably travels between a first abutment and a second abutment. The carriage may comprise a magnet and the reed switch is positioned within the shock sensor so that the reed switch is activated by the change in magnetic field exerted upon the reed switch by the magnet as the carriage travels from the first abutment to the second abutment and back again. The duration that the reed switch remains activated depends upon the sensitivity of the reed switch, the strength of the magnet, and the dwell time of the carriage, i.e. the time necessary for the carriage to travel between the first and second abutments. The shock sensors of the prior art have a relatively short dwell time. To increase the closure duration of the reed switch, the sensitivity of the contacts of the reed switch may be increased or the magnetic field of the magnet may be increased. A limitation is that as the magnetic field increases the sensitivity region increases correspondingly and the area between adjacent sensitivity regions decreases, to a point where there is no longer a "rest" position left for the magnet.